BandedPolyDataContourFilter

[PBrockmann]

Is the BandedPolyDataContourFilter could be implemented in vtk.js ?

I would like to rebuild a python vtk application that displays climate model (VTK Mapper) with vtk.js. The data structure choosen is a polydata. isolines and isocontours are possible features by using vtkContourFilter and vtkBandedPolyDataContourFilter. As visible from

With vtk.js, contours are possible from https://kitware.github.io/vtk-js/api/Filters_General_ImageMarchingSquares.html But what about filled contours ?

[jourdain]

Yes such filter could be created, but does not exist as of today. Feel free to contribute that filter to vtk.js if you like. Porting algorithms from VTK/C++ to VTK/JS is fairly straight forward. (As long as it does not imply 3D cells since those are missing and their re-implementation would take time and maybe not worth it)

[wschroed]

Caveat: I have only written a small amount of code for VTK.js including the marching cubes / marching squares algorithms. Given this limited experience here are some recent observations for what they are worth.

• As Seb says, reimplementing in VTK.js is definitely possible.
• Some of these algorithms depend on complex VTK classes like vtkEdgeTable etc. which are significant works unto themselves. An ambitious energetic person could make a major difference to VTK.js by building up some of this infrastructure (hint, hint)
• I am concerned about numerically sensitive code as I don't think we've experimented with that enough. For example, the C++ implementation includes using FLT_EPSILON, equivalents in JS must be found. The banded contour filter is just one example on many potentially numerically sensitive filters.
• Many algorithms in VTK are starting to use threaded / accelerated subsystems like vtkSMPTools and VTK-m which can easily speed things up by 10-1000X from what I've seen. My understanding is that JS struggles with parallelism for high-performance computing. Hopefully this changes at some point.
• Along the lines of performance, typed templating in C++ is also widely used. We need to experiment with JS to see what this means in terms of implementation (compiler optimization, memory usage, etc).
• Web assembly from C++ may make sense for converting some code. However there is lots of work to be done to make this process simpler and better and it is on our radar. Plus there are some things that may not be wrapped (at least not yet?) like threading etc.
• In some applications there is an argument to be made for client-server architectures -- i.e. run C++ algorithms on a big server or cloud instance, and use the relatively lightweight client (JS) to interact, render, perform less compute intensive computations.
• I worry about developing and maintaining duplicate code bases.

On Mon, Jan 21, 2019 at 11:18 AM Sebastien Jourdain < notifications@github.com> wrote:

Yes such filter could be created, but does not exist as of today. Feel free to contribute that filter to vtk.js if you like. Porting algorithms from VTK/C++ to VTK/JS is fairly straight forward.

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[thewtex]

An itk.js VTK C++ implementation is possible following https://github.com/InsightSoftwareConsortium/itk-js/issues/187.